Question:
Can we make tax free refund in Grenoble Airport? Can we get custom stamp for tax-free refund in Grenoble Airport?

Answer:
Yes, you can get a custom stamp at Grenoble Airport. But you have to ask at customs two hours before your flight leaves. As I understand it you get the tax refund later once you leave the country and you also need to fulfill some conditions. This article seems to have some good information but I don't know how up to date it is - How to Collect Your VAT (Detaxe) Refund.